Steel strip is frequently plated, painted, porcelain enameled, etc., to improve its appearance, provide corrosion protection or to otherwise obtain desirable surface characteristics for a variety of different applications. Prior to such treatments the steel is pretreated a number of different ways in order to promote optimum adhesion and coverage of the elected coating. Such pretreatments include pickling, etching, electropolishing, etc., all of which not only remove metal from the surface and reduce the thickness of the steel strip, but also create waste disposal problems for the pretreatment solutions giving rise to increased overall costs.
It is an object of the present invention to provide a process for converting the surface of a steel strip to an iron layer of different composition than the steel without reducing the overall thickness of the strip or generating solutions requiring costly waste treatment processing. It is a further object of this invention to provide a highly efficient electrochemical process for electrolytically eroding away the surface of a steel electrode-strip by dissolving it in an iron-ion-containing electrolyte, and replacing it with a substantially pure iron layer electrolytically deposited from substantially the same electrolyte whereby a steel strip is produced having a pure surface layer susceptible to a variety of subsequent treatments including, coating, heat treatment, etc., not readily performable on the steel surface itself. It is a still further object of the present invention to accomplish the foregoing objects by electrolytically eroding a steel surface while concurrently electrolytically depositing iron onto another previously eroded surface as the surfaces pass countercurrently and in close proximity one to the other through a single iron-ion-containing electrolyte. These and other objects of the invention will become more readily apparent from the detailed description which follows in which: